This invention relates to a valve actuator operated by hydraulics, pneumatics or springs or some other mechanic devices and consisting of a cylinder suitably in two sections and provided with inlet and outlet openings for operating medium, a piston moving inside the cylinder and preferably in one piece and provided with sealings at both ends, a torque shaft passing outside the cylinder, and a machine element connecting the piston and the torque shaft.
Hydraulic, pneumatic and mechanic valve actuators of several various types, changing a linear piston movement into a rotating movement controlling a valve, are previously known. All these known devices have, however, a disadvantage either in a complicated and costly construction or a great size in relation to the power.
The actuator according to the invention is characterized in that a torque shaft, at a right angle to the direction of the piston movement, and a machine element or joint connecting the torque shaft to the piston are located in the space formed inside the end flanges of the piston, the piston sealings and the cylinder walls and separated from the operating medium, and that the piston section connecting the end flanges of the piston is provided with an opening or openings for the torque shaft passing into the piston or through the piston.
When comparing the device of this invention to actuators in which the cylinders and the so called torque centre, formed by the torque shaft, the machine element connecting the torque shaft to the piston, and the casing section, are separate entities, the actuator of this invention is considerably shorter in the longitudinal direction as the torque centre is located inside the piston. Besides this, the number of parts is smaller. A third considerable advantage is the small amount of sealings or other tight connections. The only sealings required are the piston sealings. As the operating medium cannot pass into the space inside the piston, it is not necessary to seal the division plane of the cylinders or the opening where the torque shaft passes outside.